1. Field of the Invention
The present invention relates to the structure of a reinforcement plate member used in an automobile airbag apparatus for protecting a driver or passenger upon collision of a vehicle, such as a car, to thereby ensure safety. More particularly, the invention relates to an improvement in the structure of a reinforcement plate member for a fracture-opening section which breaks so as to allow unfolding and expansion of an airbag, which structure enables reliable melt-joining between the reinforcement plate member and the fracture-opening section.
2. Description of the Related Art
An airbag apparatus used in a vehicle, such as a car, basically includes an airbag, an airbag case for accommodating the folded airbag, and an inflater for inflating the airbag. The airbag apparatus is accommodated within an instrument panel on the front-passenger-seat side, or within a steering wheel or side pillar, such that the airbag apparatus faces a driver or passenger. The cover of the instrument panel includes a fracture-opening section for allowing unfolding and expansion of the airbag. The fracture-opening section has a size corresponding to that of an opening portion of the airbag case and is defined by a perforation-like fracture groove surrounding the fracture-opening section.
A reinforcement plate member formed of metal is integrally fixed to the inner wall surface of the fracture-opening section; and a hinge portion of the reinforcement plate member is connected to the instrument panel.
The thus-configured automobile airbag apparatus functions in the following manner. Upon collision of the vehicle, an impact force caused by the collision is detected by a sensor. A control unit including a CPU judges whether or not the detected impact force is equal to or higher than a predetermined value. When the control unit judges that the impact force is not lower than the predetermined value, the control unit issues a signal for causing the inflater to generate a predetermined gas. The gas is fed to the airbag so as to promptly inflate the airbag.
The inflating airbag presses, from inside, the fracture-opening portion of the instrument panel cover (hereinafter referred to as an xe2x80x9cinterior coverxe2x80x9d), including the reinforcement plate member. The fracture-opening section is fractured along a fracture groove and detached from the interior cover. The detached fracture-opening section is opened outward while being turned inside out about the hinge portion of the reinforcement plate member. Simultaneously, the inflating airbag projects outward from the interior cover through the thus-formed opening in the interior cover. Serving as a cushion, the inflated airbag supports a passenger, such as a front seat passenger, at his/her chest and head, thereby protecting the passenger from the impact force of collision.
Generally, the instrument panel of an automobile consists of an instrument panel core formed from a synthetic resin, such as polypropylene, through integral molding, and an instrument panel cover (interior cover), which covers the instrument panel core and is formed of a synthetic resin, such as polypropylene.
A conventional reinforcement plate member attached to the back surface of the fracture-opening section will be described with reference to FIGS. 1 to 3.
FIG. 1 is a perspective view of a fracture-opening section formed in an interior cover and a reinforcement plate member for reinforcing the fracture-opening section from the inner surface thereof. FIG. 2 is an explanatory sectional view of a main portion before inflation of an airbag. FIG. 3 is an explanatory sectional view of the main portion after inflation of the airbag.
As shown in FIG. 1, a reinforcement plate member 2 for reinforcing a fracture-opening section 1 has a curved shape corresponding to that of the inner wall surface of the fracture-opening section 1. The reinforcement plate member 2 has a substantially rectangular shape and an area slightly smaller than that of the fracture-opening section 1. A hinge portion 3 is formed at one end (upper end) of the reinforcement plate member 2 with respect to the transverse direction (shorter-side direction). The hinge portion 3 extends in the longitudinal direction (longer-side direction) of the reinforcement plate member 2 and is bent outward (in the direction of an arrow) as the airbag inflates. The hinge portion 3 has an intermediate portion 4 bent substantially perpendicular in a direction away from the back surface of the reinforcement plate member 2, and a connection portion 5 extending upward substantially perpendicular from the end edge of the intermediate portion 4.
A base portion 6a of a support member 6 is fixed to the connection portion 5 by means of nuts and bolts 7. The support member 6 has two support arms 6b, which extend in a direction away from the back surface of the reinforcement plate member 2. As shown in FIG. 2, the distal ends of the support arms 6b are fixed to an interior cover 9 by means of tapping screws 8, whereby the reinforcement plate member 2 is supported by the interior cover 9.
A case support member 10 is fixed to the base portion 6a of the support member 6 by means of the nuts and bolts 7. An airbag case 11 for accommodating an unillustrated airbag is fixed to the case support member 10 by means of nuts and bolts 12.
A plurality of depressions 2A are formed, for reinforcement purpose, on the reinforcement plate member 2 in such a manner as to extend in the transverse direction of the reinforcement plate member 2 and to be arranged at predetermined intervals in the longitudinal direction of the reinforcement plate member 2. Blocks of coupling holes 2B are formed in the reinforcement plate member 2 while being arranged at predetermined intervals in the transverse and longitudinal directions of the reinforcement plate member 2 over the entire surface thereof. Each block includes a plurality of coupling holes 2B extending in the transverse direction of the reinforcement plate member 2 and arranged close to one another in the transverse and longitudinal directions of the reinforcement plate member 2.
For each group of coupling holes 2B, a plurality of elongated protrusions 1A are formed on the inner wall surface of the fracture-opening section 1 of the interior cover 9 in a manner as to be aligned with the coupling holes 2B. The elongated protrusions 1A are engaged with the corresponding coupling holes 2B, and the tip ends of the protrusions 1A projecting from the back surface of the reinforcement plate member 2 are melted through application of heat, such that the tip ends are flattened. Thus, the reinforcement plate member 2 is fixedly attached to the inner wall surface of the fracture-opening section 1.
In the above-described configuration, when the unillustrated air bag inflates, the inflating airbag presses, from inside, the reinforcement plate member 2. As a result, the fracture-opening section 1 of the interior cover 9 is fractured along the fracture line and detached from the interior cover 9. Simultaneously, the hinge portion 3 of the reinforcement plate member 2 having been in the state shown in FIG. 2 is bent as shown in FIG. 3, and the case support member 10 having been in the state shown in FIG. 2 is bent as shown in FIG. 3. As a result, the detached fracture-opening section 1 having been in the state shown in FIG. 2 is opened outward as shown in FIG. 3, resulting in formation of an opening 9A in the interior cover 9. The unillustrated airbag inflates further and projects outward from the interior cover 9 through the opening 9A. Thus, the intended purpose is achieved.
However, in the conventional automobile airbag apparatus, when the fracture-opening section 1 of the interior cover 9 fractures from the fracture groove upon inflation of the airbag, the hinge portion 3 of the reinforcement plate member 2 and the case support member 10 are bent as shown in FIG. 3. Therefore, reaction forces generated when the hinge portion 3 and the case support member 10 are bent concentrate on a support-member fixing portion 9B of the interior cover 9 supporting the tapping screws 8, with the result that the support-member fixing portion 9B breaks and separates from the interior cover 9. As a result, the opening action of the fracture-opening section 1 including the reinforcement plate member 2 becomes unstable, which may hinder the inflation of the airbag through the opening 9A.
The fracture-opening section 1 and the reinforcement plate member 2 are united through a process of fitting the elongated protrusions 1A of the fracture-opening section 1 into the coupling holes 2B of the reinforcement plate member 2, and melting the tip ends of the protrusions 1A projecting from the back surface of the reinforcement plate member 2 through application of heat, such that the tip ends are flattened. Since the reinforcement plate member 2 formed of a single metal plate and the interior cover 9 formed of a synthetic resin such as polypropylene differ in coefficient of linear expansion, the following problems arise. The interior temperature of a vehicle is as high as 110xc2x0 C. in summer, and as low as xe2x88x9235xc2x0 C. in a cold region in winter. As a result, the reinforcement plate member 2 attached to the back surface of the fracture-opening section 1 of the interior cover 9 expands and contracts, resulting in generation of warpage or deformation. In this case, the reinforcement plate member 2 may separate from the back surface of the fracture-opening section 1 due to breakage of the joining portions therebetween, thereby hindering the fracture of the fracture-opening section 1 along the fracture groove and hindering the smooth opening of the reinforcement plate member 2 about the hinge portion 3. Further, cracks are formed at the edge portion of the opening 9A formed as a result of fracture of the fracture-opening section 1, and in the worst case, the fracture-opening section scatters.
The present invention has been accomplished in order to solve the above-mentioned problems, and an object of the present invention is to provide an improved structure for a reinforcement plate member used in an automobile airbag apparatus, which structure eliminates adverse effects, such as generation of warpage, on the joint portion between a fracture-opening section of an interior cover and a reinforcement plate member, which would otherwise be caused when the reinforcement plate member is formed of a metal having a coefficient of expansion different from that of the fracture-opening section. The structure of the present invention enables smooth fracture and opening of the fracture-opening section, prevents formation of a clearance between the fracture-opening section and the reinforcement plate member, and prevents scattering of the fracture-opening section which would otherwise result from breakage of the joint portion between the fracture-opening section of the reinforcement plate member.
The present invention provides an automobile airbag apparatus disposed within an instrument panel, steering wheel, or side pillar covered with an interior cover, comprising an airbag case having an opening portion located in opposition to a back surface of the interior cover; an airbag accommodated within the airbag case in a folded state, the airbag being able to be inflated by means of gas from an inflater; a fracture-opening section defined in the interior cover to be located in opposition to the opening portion of the airbag case, the fracture-opening section being defined by at least a fragile groove formed from the back surface of the interior cover to surround the fracture-opening section; and a reinforcement plate member attached to a back surface of the fracture-opening section through deformation of a portion of the fracture-opening section through application of heat thereto, the reinforcement plate member having a shape corresponding to that of the fracture-opening section. In the airbag apparatus, the reinforcement plate member has a main-body portion attached to the back surface of the fracture-opening section and an attachment portion extending from the main-body portion via a hinge portion; and a deformation absorbing structure is formed at least in the main-body portion of the reinforcement plate member.
In the structure according to the present invention, even when the reinforcement plate member is formed of a metal having a coefficient of expansion different from that of the fracture-opening section, the joint portion between the fracture-opening section and the reinforcement plate member does not suffer adverse effects, such as generation of warpage, which would be otherwise caused by variation in temperature. Accordingly, fracture and opening of the fracture-opening section can be effected smoothly, and no clearance is formed between the fracture-opening section and the reinforcement plate member. Further, it becomes possible to prevent scattering of the fracture-opening section, which would otherwise result from breakage of the joint portion.
Moreover, since deformation of the reinforcement plate member is suppressed, the reinforcement structure for suppressing deformation can be omitted, so that the part can be produced at reduced cost.
In another airbag apparatus according to the present invention, a reinforcement rib projects from the back surface of the interior cover, the reinforcement rib having engagement holes located at predetermined intervals in the longitudinal direction and a breakable portion in the vicinity of a connection corner portion through which the reinforcement rib is connected to the interior cover; the reinforcement plate member has an attachment portion extending from a main-body portion via a hinge portion and having attachment holes formed in the attachment portion at positions corresponding to those of the engagement holes; hooks fixed to the airbag case are engaged with the attachment holes and the engagement holes; and a deformation absorbing structure is formed in at least in the main-body portion of the reinforcement plate member.
In still another airbag apparatus according to the present invention, the fracture-opening section is defined by a fragile contour portion surrounding the fracture-opening section and a fragile splitting portion for dividing the fracture-opening section into first and second subsections; first and second reinforcement plate members are attached to back surfaces of the first and second subsections, each of the first and second reinforcement plate members having a main-body portion and an attachment portion extending from the main-body portion via a hinge portion; a reinforcement rib projects from the back surface of the interior cover, the reinforcement rib having engagement holes at predetermined intervals in the longitudinal direction; at least one of the first and second reinforcement plate members has attachment holes formed in the attachment portion at positions corresponding to those of the engagement holes; hooks fixed to the airbag case are engaged with the attachment holes and the engagement holes; and a deformation absorbing structure is formed in at least in the main-body portion of each of the first and second reinforcement plate members.